This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Poloxamer, a family of surface-active block copolymers comprising a hydrophobic poly (propylene oxide) (PPO) moiety capped with hydrophilic poly (ethylene oxide) (PEO) moieties on the two ends, is known to help seal permeabilized cell membranes that are damaged by disease or trauma and arresting leakage of intracellular materials of the damaged cell. Despite poloxamer's importance in restoring cell membrane integrity, the underlying sealing mechanisms are not well understood. Poloxamer 188 (P188, molecular weight = 8400 g/mol, with 80 wt% PEO) was the first among its family tested to be a membrane sealant due to its wide application in pharmaceuticals with low toxicity. Besides, P188 is an efficient gene carrier with gene transfer accomplished via endocytosis. P188 and other poloxamers have also been included in drug delivery systems to sterically stabilize liposomes by prolonging their circulation time. Improvement of poloxamer design for pharmaceutical use relies on a better understanding of interactions between poloxamer and lipid membranes.